Path loaders of this kind are used especially in timber harvesters. The loader carries various timber handling devices, such as a harvester component, a timber felling head, or a timber grab. The characteristics of such a loader allow it to be used to successfully perform desired operations in timber harvesting and tree felling. The predominant methods are forest thinning and final felling. The loader is generally installed on the chassis of the timber harvester by means of bolts running through a flange plate.
The use of a timber loader is previously known in a forestry machine, which loader includes a separate lifting boom and a hinged boom, as well as hydraulic cylinders operating the booms, and in which the booms operate independently of each other. Thus, the paths of the main boom and the hinged boom are not connected to each other. Thus, to create a desired path, two separate control movements must be made simultaneously. Timber harvesting usually involves an essentially horizontal path. Such a path is quite difficult to achieve by manual operation, which generally results in a path that bounces up and down, which is detrimental to both the load and the equipment.
Publication U.S. Pat. No. 5,197,615 discloses a so-called wide-angle joint, in which the movements of the booms are also connected to each other. Besides having a wide angle, this joint mechanism can resolve the aforementioned problem. By using only a single hydraulic cylinder, the free end of the pendulum boom makes an essentially horizontal movement (FIG. 4). The same figure also shows a typical wide-angle joint construction, in which the outer boom is operated by means of an arm that is separately attached to the inner boom with the aid of a connector bar.
International patent publication WO97/41056 discloses a loader showing two other joint mechanisms that can resolve the aforementioned problem. The joint mechanism of the wide-angle joint featured in FIG. 1 has a construction that is simple, but which demands extremely precise dimensioning. FIG. 2 shows a simplified version of the joint construction, in which the operations of the booms are connected together. In this case, the lower end of the hydraulic cylinder operating the hinged boom is pivoted to the main boom and the upper end is pivoted to the hinged boom's extension, which forms a straight arm operating the hinged boom. It should be noted in this case that the main boom, the hinged boom extension, and the cylinder form a triangle, in which the angle between the two sides of constant length is altered by altering the length of the cylinder. In the case of FIG. 2, the paths of the booms are connected to each other by means of the lifting cylinder, in such a way that its lower end is pivoted in a known manner to the base and its upper end to an extension of the hinged boom, in fact to the same pin as the manoeuvring cylinder.